This invention relates to a back-up clamp component for use in a back-up clamp for the welding of pipelines.
Pipelines are in widespread use for the transportation of fluids such as water, gas and oil. Many such pipelines are of metal and are manufactured in lengths which must be assembled on site into the complete pipeline. To connect two adjacent lengths of pipe together it is usual to provide a welded joint. Thus, a new length of pipe is placed close to the end of the existing pipeline and a welded joint is formed therebetween (it is usual for a small gap to be present between the adjacent pipe ends prior to welding, which gap is filled by the weld). A subsequent length of pipe is then placed against the new end of the (extended) pipelipe, and the procedure is repeated.
To ensure an accurate and effective weld it is necessary that the two adjacent pipe ends be maintained in alignment during welding. In addition, a known concern with such welded joints is that weld material can be spattered through the gap and into the interior of the pipe, and can impair the subsequent flow of fluid therealong. It is therefore known to insert a back-up clamp into the pipeline adjacent the joint to be welded, the clamp serving to align the two pipe ends and also having a number of shoes which can be moved to lie beneath the gap and prevent any weld spatter from entering into the pipeline. Copper has been found to be a preferred material for the shoes, and in particular copper xe2x80x9c101xe2x80x9d.
A back-up clamp of the type described is disclosed in WO 95/21721. The back-up clamp comprises two sets of clamping members which are adapted to engage the respective pipes adjacent their ends and to assist the alignment of the pipe ends. Between the clamping members is a ring of copper shoes which is adapted to lie underneath the gap during welding. The clamping members and the copper shoes are movable between a retracted condition in which the back-up clamp can be moved along the pipeline, and an extended condition in which the clamping members and the copper shoes engage the inside surface of the respective pipes, the copper shoes lying immediately beneath the gap. The clamping members are moved inwardly and outwardly by a toggle mechanism actuated by pneumatic means. The copper shoes are urged into their extended condition by springs, and into their retracted condition by hooks carried by the clamping shoes.
It is a recognised disadvantage of the known device that it can only be used for larger diameter pipelines, i.e. those of around 8 inches (20.3 cm) diameter or greater, the size of the mechanical toggle linkages effectively providing the lower limit to the size of the device and thus the pipelines upon which the device can be used.
In addition, it is known that debris or other matter within the pipeline adjacent the gap can cause a copper shoe to fail to make contact with the wall of the pipe, so that weld spatter can subseqently enter the pipeline adjacent that shoe. Thus, since it is only the relatively weak spring force that is urging the copper shoes into contact with the pipeline this force cannot overcome certain debris in the path of the shoe.
Furthermore, because the clamping members are required to ensure the alignment of the pipe ends they are necessarily located close together (so that each can be located close to the end of its respective pipe). The need to locate the clamping members close together significantly limits the design freedom for the copper shoes (which lie between the clamping members). In addition, since the clamping shoes are located close to the ends of their respective pipes, whilst they can seek to ensure that the ends of the pipes are substantially concentric, they cannot necessarily ensure complete alignment of the pipes, since the longitudinal axes of the pipes may not be parallel. If the longitudinal axes of the pipes are not parallel the size of the gap will vary around the circumference of the pipeline, so that the effectiveness and reliability of the weld may be impaired.
Also, since the clamping members are not located at the very ends of the respective pipes, some misalignment (i.e. a lack of concentricity of the pipe ends) may be present, which misalignment can cause discontinuities or lips internally of the pipeline; clearly the presence of such discontinuities is likely to cause vortices and thus pressure drops along the pipeline (which pressure drops can accumulate and become considerable in a long pipeline).
GB Patent Application 2,067,945 also discloses a back-up clamp of the general type described. In this design also, the back-up shoes are urged into contact with the pipeline by spring force alone, so that the disadvantages of such an arrangement outlined above are shared by the devices of this disclosure. The back-up shoes are located adjacent (and indeed are carried by) the clamping members, and so the device is less well able to correctly align the longitudinal axes of the pipes which are to be welded.
U.S. Patent 5,110,031 discloses a back-up clamp in which the back-up shoes are of a ceramic material. In this document the clamping members and the back-up shoes are moved radially by respective radially acting pistons. It is indicated that the pistons are actuated by pneumatic or hydraulic means. No means is disclosed for the retraction of the clamping members or the back-up shoes.
GB Patent 1,528,775 discloses a back-up clamp in which the clamping members are actuated by way of a toggle mechanism, i.e. a piston is moved longitudinally by hydraulic or pneumatic pressure, and the longitudinal movement is converted to radial movement of the clamping members by mechanical links. The back-up shoes are however moved radially by radially acting piston and cylinder arrangements. Hydraulic or pneumatic pressure can be fed to both sides of the piston to effect forced extension and retraction of the back-up shoes.
Utilising hydraulic or pneumatic pressure to drive out the back-up shoes avoids the disadvantages outlines above for those disclosures relying upon spring force alone. The most significant advantage is that the force which can be exerted upon the pipeline (or rather the ends of the adjacent pipes which are to be welded together) is much increased, allowing the back-up shoes to contribute to the alignment of the pipes. This in turn permits the clamping members to be spaced further from the ends of the respective pipes than would otherwise be possible, increasing the likelihood that the longitudinal axes of the pipes are aligned.
There is also a significant advantage in driving the back-up shoes both outwardly and inwardly, i.e. rather than relying upon spring force to achieve the inward retraction movement, for example. Thus, when the back-up shoes are positively driven inwardly by hydraulic or pneumatic pressure there is far less likelihood of the back-up shoes xe2x80x9cstickingxe2x80x9d in their extended condition. Should the back-up shoes stick in their extended condition it would be difficult or perhaps impossible to move the clamp along the pipeline.
Notwithstanding the advantages of the device as disclosed in U.K. Patent 1,528,775, it is not in widespread use; and this is believed to be because of the complexity of the device. Thus, the device is mechanically complex, and also requires complex and numerous hydraulic and/or pneumatic connections to be made to communicate the pressurised fluid to the sites upon the clamp at which it is required.
In addition, the pressurised fluid is fed to the cylinder housing the piston of the back-up shoe by way of hoses connected to the clamp body immediately beneath the back-up shoe. With clamps for larger-diameter pipelines there is usually enough space to accommodate the hoses and permit access to the hose connections, but this becomes increasingly difficult to achieve as the diameter of the pipeline, and thus the diameter of the clamp, becomes smaller.
In addition, the hoses pass around a part of the clamp body, and are therefore susceptible to damage. Accordingly, great care has to be taken, both during use of the clamp and also during on-site and off-site handling, to ensure that no damage is caused to the hoses. If any damage is caused to a hose, this might not become apparent until the clamp is in use, perhaps preventing the back-up shoes operating for example; this will result in considerable wastage of time whilst the clamp is retrieved from within the pipeline, and repaired.
Should a hose become damaged, in order to repair the clamp a replacement hose is required to be available, and this might not always be the case on site.
Finally, should the hoses delivering fluid to both sides of the piston become damaged and require replacement, it is essential that they are correctly connected so that the fluid is communicated to the correct location of the clamp.
It is the object of the present invention to provide a back-up clamp component, and in particular a support section for the back-up shoes, which in use avoids or reduces the disadvantages with the prior devices described above.
According to the invention therefore there is provided a back-up clamp component carrying a number of shoes which can be moved radially inwardly and outwardly, the shoes being connected to respective piston and cylinder arrangements, the axis of each piston and cylinder arrangement being substantially radial, there being means to introduce pressurised fluid to both sides of the piston so that the shoes can be positively driven outwardly and inwardly, the means to introduce pressurised fluid to both sides of the piston including respective conduits within the body of the component, characterised in that the conduits open at an end face of the component.
For the avoidance of doubt, an end face is one of the two generally flat faces of the component which in the assembled back-up clamp will engage adjacent clamp sections.
Because the conduits terminate at an end face of the component, the component is suited to use with a back-up clamp in which the fluid conduits are located within the clamp, such as that disclosed in our co-pending GB patent application for a xe2x80x9cBack-Up Clampxe2x80x9d. In such arrangements, the component is adapted to be secured to an adjacent clamp section having conduits which themselves open at a corresponding end face of the respective section so that when the component and adjacent section are secured together the conduits line up and fluid can flow from the conduit of the adjacent section to the conduit of the component, and vice versa.
Such an arrangement avoids the requirement for hoses external to the clamp body, so eliminating the likelihood of damage thereto.
Preferably, the piston and cylinder arrangements are connected to a source of pneumatic pressure; alternatively they may be connected to a source of hydraulic pressure.
Therefore, the shoes of the back-up clamp component according to the invention can be urged to their clamping position by pneumatic or hydraulic pressure. In the case of pneumatic pressure a,compressor providing perhaps 200 psi can readily be provided so that the shoes are urged outwardly with far greater force than is available with the prior art xe2x80x9cspring-biassedxe2x80x9d devices. Accordingly, the force with which the shoes are moved will assist in ensuring that the pipe ends are concentric, the component forcing those pipe ends into alignment.
Preferably, the body of the component is annular and an internal collar is located therein. Preferably also the collar has a flange. Desirably, the flange has a part of a conduit therein; desirably also the flange provides a part of an end face of the component. Usefully, the collar includes a recess means through which pressurised fluid can be communicated to one side of the piston.
Usefully also, the collar includes an annular depression aligned with the axis of the cylinders, the annular depression ensuring that a substantially equal pressure is imparted to each of the pistons.
Preferably, sealing means is provided between the collar and the body of the component.
Preferably, a cap member is provided for each cylinder, the cap member having an opening through which the piston stem an project. Preferably also, the cap member covers a part of the body of the component, the means to introduce pressurised fluid to the second side of the piston including a conduit which opens into said part of the body of the component. Preferably also, the cap member includes a recess means by which fluid can flow from said conduit into the cylinder.
Desirably each shoe is connected to a respective carrier member, each carrier member having a shoulder which can engage an adjacent shoe. Accordingly, if one of the piston and cylinder arrangements should fail to operate (i.e. to move outwardly), or be slow to operate, its respective shoe can nevertheless be moved to its clamping position by the adjacent carrier members. This will also assist if there is any dirt or debris hindering the movement of one of the shoes, three adjacent carrier members can act to urge the shoe towards its clamping condition so pushing any dirt or debris out of the way. Similarly, the two adjacent shoes can help to drive back the intermediate shoe by way of their engagement with the carrier member of that shoe.
Preferably, each carrier member is slidably mounted to a link member, the carrier member being longitudinally movable relative to the link member. Preferably also, each carrier member is resiliently biassed relative to its link member, adjacent carrier members being biassed in opposite directions.
Usefully, the shoes are of isosceles trapezium or triangular form, having angled edges, with adjacent shoes being oppositely directed. The edges of each shoe may therefore be maintained in permanent engagement with the adjacent shoes. The shoes are preferably biassed so that as they move inwardly and outwardly their edges slide relative to the edges of the adjacent shoes, but are maintained in contact therewith. Maintaining the edges between adjacent shoes in contact reduces the likelihood of dirt or debris entering between the edges, and so reduces the likelihood that the shoes cannot together form a circular periphery.